1. Technical Field
The present invention relates to a document camera having an audio signal acquisition unit and a camera unit, and to a video and audio output system and a video and audio output method.
2. Related Art
According to a related art, an image display system having a document camera and a projector directly connected to the document camera via a USB interface is known (see JP-A-2010-177736). The document camera picks up an image of a target object and transmits a stream of the picked-up image (video signal) to the projector. The projector receives the stream, carries out image processing on the image of the stream, and then executes projection of the processed image. In this image display system, since the document camera and the projector are directly connected to each other via the USB interface without using a computer in-between, even a user who is unaccustomed to machine operation can easily operate the system.
Incidentally, with respect to the image display system of this type, a configuration in which the document camera further includes a video recording unit for recording a video signal so that the video signal is recorded or played back is known. Also, a configuration in which the document camera further includes an audio signal acquisition unit for acquiring an audio signal so that the audio signal is recorded or played back together with the video signal is known. In such configurations, a time stamp for synchronizing the video signal with the audio signal is added by the USB (Universal Serial Bus) interface. That is, the projector synchronizes the video signal with the audio signal based on the time stamp and thus outputs these signals.
Also, in such configurations, outputting the video signal and the audio signal acquired by the document camera, in real time from the projector utilizing a part of the video recording (audio recording)/playback function for the video signal and the audio signal (sound reinforcement function), is considered.
However, in such configurations, since the projector synchronizes the video signal with the audio signal based on the time stamp and thus outputs these signals, one of the signals is outputted with a delay in accordance with the other signal which takes a longer processing time. Therefore, there is a problem that the audio signal, in particular, is outputted with an extremely large delay from the time point of audio acquisition. This is not practical for the sound reinforcement function.